Alight emitting diode display which uses a light emitting diode (LED) as a light emitting unit (light emitting device) has been actively developed. In the light emitting diode display, a light emitting unit formed of a red light emitting diode functions as a red light emitting sub-pixel, and a light emitting unit formed of a green light emitting diode functions as a green light emitting sub-pixel. Also, a light emitting unit formed of a blue light emitting diode functions as a blue light emitting sub-pixel. A color image is displayed according to the light emitting states of the three kinds of sub-pixels.
Also, an organic EL display for using an organic electro luminescence (EL) element as the light emitting unit has been known. In the organic EL display, as a drive circuit for driving the light emitting unit, a variable constant current driving method of which a light emission duty is fixed has been widely used. Also, in order to reduce unevenness of light emission, the organic EL display has used a pulse width modulation (PWM) method (for example, refer to Patent Document 1). In the PWM driving method, a sawtooth waveform voltage having a sawtooth waveform (ramp waveform) voltage change is used, and the sawtooth waveform voltage is compared with an analog video signal voltage. Then, a light emitting period of the light emitting unit (light emitting element) is determined based on the comparison result.